Placeholder and emptyText fixes, little bit of PSR-2

1) no more default emptyText message for Model field
2) set default_empty_text message for ValueList fields
3) PSR-2 of ValueList
4) set ValueList as actually abstract class
5) simplify ValueList->getValueList()
ValueList: use normalize() instead of loadPOST()

That doesn't change much, but should be more correct to do this way. loadPOST() is more like "internal" or "core" method, but normalize() is function meant for customization.
Merge pull request #399 from DarkSide666/master

Placeholder and emptyText fixes, little bit of PSR-2